Definition 3.1 [1]}
Let \(\mathcal {A}= (a_{i_1 i_2 i_3 ...i_m}) \in T_{m,n}\)  and \(J\subseteq [n]\)  with \(|J|=r, 1\le r \le n\) . Then a principal subtensor of \(\mathcal {A}\)  is denoted by \(\mathcal {A}^J_r\)  and is defined as
\( \mathcal {A}^J_r = ( a_{i_1 i_2 ...i_m} ), \; \forall \; i_1, i_2,...i_m \in J .\) 

